Computer disk drives store information on magnetic disks. Typically, the information is stored on each disk in concentric tracks, divided into sectors. Information is written to and read from a disk by a transducer (or head), which is mounted on an actuator arm capable of moving the transducer radially over the disk. Accordingly, the movement of the actuator arm allows the transducer to access different tracks. The disk is rotated by a spindle motor at a high speed, allowing the transducer to access different sectors on the disk. The transducer may include separate or integrated read and write elements.
A diagrammatic representation of a conventional disk drive, generally designated 10, is illustrated in FIG. 1. The disk drive comprises a disk 12 that is rotated by a spindle motor 14. The spindle motor 14 is mounted to a base plate 16. An actuator arm assembly 18 is also mounted to the base plate 16. The disk drive 10 also includes a cover (not shown) that is coupled to the base plate 16 and encloses the disk 12 and actuator arm assembly 18.
The actuator arm assembly 18 includes a flexure arm 20 attached to an actuator arm 22. A transducer 24 is mounted near the end of the flexure arm 20. The transducer 24 is constructed to magnetize the disk 12 and to sense the magnetic field emanating therefrom. The actuator arm assembly 18 pivots about a bearing assembly 26 that is mounted to the base plate 16.
Attached to the end of the actuator arm assembly 18 is a magnet 28 located between a pair of coils 30. The magnet 28 and coils 30 are commonly referred to as a voice coil motor 32 (VCM). The spindle motor 14, transducer 24 and VCM 32 are coupled to a number of electronic circuits 34 mounted to a printed circuit board 36, which comprise the control electronics of the disk drive 10. The electronic circuits 34 typically include a read channel chip, a microprocessor-based controller and a random access memory (RAM) device.
The disk drive 10 typically includes a plurality of disks 12 and, therefore, a plurality of corresponding transducers 24 mounted to flexure arms 20 for the top and bottom of each disk surface. However, it is also possible for the disk drive 10 to include a single disk 12 as shown in FIG. 1.
FIG. 2 is a diagrammatic representation of a simplified top view of a disk 12 having a surface 42 which has been formatted to be used in conjunction with a conventional sectored servo system (also known as an embedded servo system), as will be understood by those skilled in the art. As illustrated in FIG. 2, the disk 12 includes a plurality of concentric tracks 44a–44g for storing data on the disk's surface 42. Although FIG. 2 only shows a relatively small number of tracks (i.e., 7) for ease of illustration, it should be appreciated that typically many thousands of tracks are included on the surface 42 of a disk 12.
Each track 44a–44g is divided into a plurality of data sectors 46 and a plurality of servo sectors 48. The servo sectors 48 in each track are radially aligned with servo sectors 48 in the other tracks, thereby forming servo wedges 50 which extend radially across the disk 12 (e.g., from the disk's inner diameter 52 to near its outer diameter 54). The servo sectors 48 are used to position the transducer 24 associated with each disk surface 42 during operation of the disk drive 10. The data sectors 46 are used to store customer data. Servo sectors 48 contain information relating to both their radial location and circumferential location on the disk surface 42.
As is well known to those skilled in the art, servo sectors 48 are written during a servo track writing process. In the servo track writing process, a clock head is used to write a clock track on the disk surface 42. The clock track includes a clock track index, which is used as an initial circumferential reference point on the disk surface 42.
Servo sectors 48 are written onto the disk surface 42 relative to the clock track index (in their circumferential sense), so that they form the servo wedges 50 described above. Since the clock track index is only used during the servo writing process, a servo sector index is created to designate a circumferential position on the disk surface (e.g., sector 0 for each of the tracks). It should be understood that the servo sector index is not necessarily located at the same position as the clock head index, but may be some predefined (but arbitrary) circumferential distance therefrom.
Since information relating to the radial and circumferential position of a servo sector is located in the servo sector itself, such information may only be obtained when a transducer flies proximate to the servo sector. Thus, the location of the servo sector index may only be obtained when the transducer is flying over (or under) servo sectors.
There are instances, however, when transducers are not flying over (or under) servo sectors. In such cases, a servo sector index relating to a circumferential position on the disk surface 42 is generally not available.
Referring again to FIG. 1, the flexure arm 20 is manufactured to have a bias such that if the disk 12 is not spinning, the transducer 24 will come into contact with the disk surface 42. When the disk is spinning, the transducer 24 typically moves above, or below, the disk surface at a very close distance, called the fly height. This distance is maintained by the use of an air bearing, which is created by the spinning of the disk 12 such that a boundary layer of air is compressed between the spinning disk surface 42 and the transducer 24. The flexure arm 20 bias forces the transducer 24 closer to the disk surface 42, while the air bearing forces the transducer 24 away from the disk 12 surface. Thus, the flexure arm 20 bias and air bearing act together to maintain the desired fly height when the disk 12 is spinning.
If the disk 12 is not spinning at a requisite rate, the air bearing produced under the transducer 24 may not provide enough force to prevent the flexure arm 20 bias from forcing the transducer 24 to contact the disk surface 42. If the transducer 24 contacts an area on the disk 12 surface that contains data, some of the data may be lost. To avoid this, the actuator arm assembly 18 is generally positioned such that the transducer 24 does not contact a data-containing area of the disk surface 42 when the disk 12 is not spinning, or when the disk 12 is not spinning at a sufficient rate to maintain an air bearing.
With reference again to FIG. 2, the disk surface 42 includes a landing zone 56 where no data or servo information is stored and, therefore, where no servo sector index information is available. As will be understood by those skilled in the art, the landing zone 56 is where a transducer 24 of a contact start/stop disk drive will land when the drive is powered down. Furthermore, in the case of a load/unload drive, the landing zone 56 is an area that is reserved (for safety-sake) for the transducer 24 to contact when being loaded onto and unloaded from the disk surface 42.
The disk drive of FIG. 1, which is a load/unload type disk drive, includes a ramp tab 58 that is attached to the end of the flexure arm 20. The ramp tab 58 engages a ramp 60 when the actuator arm assembly 18 is unloaded from the disk surface 42. Unloading the actuator arm assembly 18 from the disk surface 42 prevents the bias from the flexure arm 20 from forcing the transducer 24 into contact with the disk 12 surface when the disk 12 is not spinning, thus helping to avoid data loss.
With reference now to FIG. 3, a diagrammatic representation illustrating a side view of a simple ramp 60 is now described. The ramp 60 has an upper ramp portion 62 and a lower ramp portion 64. Thus, when the ramp tab 58 engages the upper or lower ramp portion 62,64, it moves along the ramp 60 and into a parked position. Located at the end of the ramp 60 farthest away from the disk 12 is a crash stop 66. The crash stop 66 acts to prevent the actuator arm assembly 18 from traveling beyond its range of motion, which can cause damage to the actuator arm assembly 18.
Because the servo sector index, which relates to a circumferential position on the disk surface, is unavailable when a transducer of a load/unload drive is parked on its ramp or when a transducer of a contact start/stop drive is parked in its landing zone, it would be advantageous to provide a circumferential index relative to the disk surface prior to loading the transducer onto the disk surface. Furthermore, it would be beneficial to provide a circumferential index relative to the disk surface in the absence of a transducer reading a servo sector index from the disk surface. In addition, it would be beneficial to use a circumferential index to reduce the landing zone for a load/unload drive, so that more information can be stored on a disk surface.